The invention relates generally to medical implants used to regulate the flow of fluids within the body. The invention may be applied, for example, to ophthalmic implants for treatment of glaucoma. The invention also relates to methods of manufacturing such implants and to delivery devices for implanting such implants.
Medical implants used to regulate the flow of fluids within the human body are known and used.
One application for the use of such implants is in the treatment of glaucoma. Glaucoma is an eye condition characterized by an increase in the intraocular pressure (IOP) of the eye to an abnormal level. A normal eye maintains a proper IOP by the circulation within the eye of aqueous humorxe2x80x94aqueous humor is secreted from the ciliary body, passes through the pupil into the anterior chamber of the eyeball, and is filtered out of the eyeball via the trabeculum and the Canal of Schlemm. With glaucoma, the aqueous humor excretory pathway is blocked, the aqueous humor cannot pass out of the eyeball at an adequate rate, the IOP rises, the eyeball becomes harder, and the optic nerve atrophies by the pressure applied on its fibers leaving the retina. A characteristic optic neuropathy develops, resulting in progressive death of the ganglion cells in the retina, restriction of the visual field, and eventual blindness. Advanced stages of the disease are characterized also by significant pain.
Glaucoma treatment, if initiated early in the course of the disease, can prevent further deterioration and preserve most of the ocular functions. The goal of glaucoma treatment is to reduce the IOP to a level which is considered safe for a particular eye, but which is not so low as to cause ocular malfunction or retinal complications.
One type of glaucoma treatment is filtration surgery, which provides an alternate route for aqueous humor to exit the anterior chamber of the eyeball and enter the sub-conjunctival space, thereby lowering the IOP. In full thickness operations a fistula is created through the limbal sclera, connecting directly the anterior chamber of the eyeball and the sub-conjunctival space. Full thickness operations provide long-lasting control of IOP; however, excessive loss of aqueous humor from the eyeball during the early postoperative period frequently leads to hypotony.
In guarded filtration surgery (trabeculectomy), a fistula created through the limbal sclera is protected by an overlying partial thickness sutured scleral flap. The scleral flap provides additional resistance to excessive loss of aqueous humor from the eyeball, thereby reducing the risk of early postoperative hypotony. However, trabeculectomy may result in higher eventual IOP and increased risk of late failure of filtration, compared with full thickness operations.
In accordance with one recently introduced procedure, a full thickness filtering fistula may be created by a holmium laser probe, with minimal surgically induced trauma. After retrobulbar anesthesia, a conjunctival incision (approximately 1 mm) is made about 12-15 mm posterior to the intended sclerostomy site, and a laser probe is advanced through the sub-conjunctival space to the limbus. Then, multiple laser pulses are applied until a full thickness fistula is created. This technique has sometimes resulted in early hypotony on account of a difficulty in controlling the sclerostomy size. In addition, early and late iris prolapse into the sclerostomy has resulted in abrupt closure of the fistula and eventual surgical failure. Further, despite its relative simplicity, the technique still necessitates the use of retrobulbar anesthesia to avoid pain caused by the laser applications. The injection of anesthetic material close to the already damaged optic nerve may sometimes lead to further visual damage. A further disadvantage of this procedure, as well as other types of glaucoma filtration surgery, is the propensity of the fistula to be sealed by scarring.
Various attempts have been made to overcome the problems of filtration surgery, for example, by using ophthalmic implant devices. Typical ophthalmic implants utilize drainage tubes so as to maintain the integrity of the openings formed in the eyeball for the relief of the IOP.
Typical ophthalmic implants suffer from several disadvantages. For example, the implants typically utilize a valve mechanism for regulating the flow of aqueous humor from the eyeball; defects in and/or failure of such valve mechanisms could lead to excessive loss of aqueous humor from the eyeball and possible hypotony. The implants also tend to clog over time, either from the inside by tissue, such as the iris, being sucked into the inlet, or from the outside by the proliferation of cells, for example by scarring. Additionally, the typical implant insertion operation is complicated, costly and takes a long time.
U.S. Pat. No. 3,788,327 to Donowitz et al. shows a prior art implant utilizing a valve mechanism for regulating the flow of aqueous humor from the eyeball. As stated above, defects in and/or failure of such a valve mechanism could lead to excessive loss of aqueous humor from the eyeball and possible hypotony. Additionally, both the inlet opening and the outlet opening in the implant shown in U.S. Pat. No. 3,788,327 may be susceptible to cloggingxe2x80x94the inlet opening by the iris and the outlet opening by scarring. Finally, implantation of an implant according to U.S. Pat. No. 3,788,327 may involve the separate steps of first providing a tract for receiving the. implant and/or suturing the implant once it is in place, which add time and possible complications to the operation.
It is an object of the invention to provide an improved implant to regulate the flow of fluids within the body. The invention may be applied, for example, to an ophthalmic implant which may be implanted into the eyeball for the treatment of glaucoma. It is a further object of the invention to provide a method of manufacturing such an implant and a delivery device for implanting such an implant.
In one embodiment of an improved implant in accordance with the invention, an intraocular implant is provided to be implanted in the eyeball. The implant includes a tube having an inlet end, an outlet end, and a tube passage therebetween for permitting aqueous humor to flow out of the eyeball, and a disk connected to the tube at the outlet end of the tube. The tube passage may have a cross-sectional area sufficiently small to inhibit the flow of aqueous humor through the tube passage. A flow controlling wire or rod may be inserted within the tube passage to provide further control over the flow. The configuration of the flow controlling rod may be selected in accordance with the desired flow characteristics. The configuration may be chosen to prevent flow when the IOP is below a threshold amount.
The disk, which is designed to be located underneath the conjunctiva, may have an outer rim for forming a reservoir having an enlarged cross-sectional area relative to the cross-sectional area of the tube passage. When aqueous humor flows through the tube passage, a bleb of aqueous humor forms under the conjunctiva so that the bleb and the elasticity of the conjunctiva assist in regulating the flow of aqueous humor through the tube as a function of the IOP.
To prevent clogging of the implant, the tube at its inlet end may be provided with a beveled surface which faces away from the iris when the implant is inserted. Additionally, one or more circumferential holes may be provided along the tube for allowing aqueous humor to flow into the tube passage even if the axial inlet opening is blocked. The hole or holes may be selectively permanently or temporarily occluded to give desired flow characteristics.
To prevent clogging at the outlet end, the disk may have an outer rim as described above which raises the conjunctiva away from the axial outlet of the tube passage to allow outflow. One or more inner uprights (which may be in the form of an inner rim) may also be provided on the disk for this purpose. Clogging is further avoided by implanting the implant under the conjunctiva at a distance away from an insertion slit in the conjunctiva, such that healing of the slit does not cause scar tissue to form in the area of the axial outlet opening of the implant.
Implantation may be facilitated by further features of the implant. For example, the implant may have one or more retention projections (for example, in the form of a spur, flange, or plate). The retention projection may be rigid, or it may be made of an elastic material such that it is able to be flexed inward against the tube during penetration through the sclera. Alternatively, the retention projection may be designed to lie initially relatively flat against the tube for easier penetration through the sclera and to prevent tearing of the sclera, with a mechanism for extending the retention projection outwardly when the implant is implanted in the eyeball. For example, the retention projection may be extended outwardly by a separate expansion tool or may be constructed of a shape memory material, such as PMMA or nitinol, so that it is extended outwardly when subjected to the heat of the eyeball. One or more such retention projections are sufficient to reliably anchor the implant in the eyeball without the need for sutures, saving time and costs.
Implantation may also be facilitated by the provision of one or more markers on the implant visible through the cornea upon passing through the sclera. For example, a circumferential hole as described above may serve as a marker; alternatively, the marker may be some other suitable visible mechanism, such as a scratch or colored mark on the tube. The visibility of the marker lets the doctor know that the marker has passed through the sclera, indicating that the implant is in place.
Implantation of an implant may be performed by use of a delivery device comprising a handle and a rodlike instrument, for example a needle or probe, for carrying the implant for insertion. The delivery device has a tip for insertion into the tube passage of the implant and a suitable retention mechanism for preventing the implant from moving up the delivery device during implantation. The retention mechanism may also be constructed to prevent the implant from rotating during implantation to insure proper orientation of the implant. The delivery device may additionally have a suitable expansion tool for extending one or more retention projections of the implant outwardly once the projection or projections have penetrated through the desired tissue.
In an embodiment of a delivery device according to the invention, the rodlike instrument has a central bore in which is located a retractable wire. The retractable wire penetrates a tube passage of the implant when the implant is attached to the delivery device. A hook on the delivery device prevents the implant from moving down the wire. After the implant is in position in the desired implantation site, the retention wire is retracted out of the implant. With the retention wire retracted, the implant is then free to slide away from the hook, allowing the delivery device to be withdrawn, leaving the implant in place.
In one method of implanting an implant according to the invention, a small slit is cut in a portion of the conjunctiva which normally lies at a distance away from the intended implantation site. As the implant itself is very small, the slit also may be very small, for example about 2 mm in length or less. The small size of the slit as well as its positioning at a distance away from the implantation site, for example about 10 mm, helps prevent contamination of the sclerostomy site and reduces the risk of infection.
The implant is placed through the slit, directed to the implantation site, and inserted into the sclera at the implantation site. The sclera may be pierced either by a needle-like tip of the tube of the implant formed by a beveled surface at the inlet end of the tube as described above or by the tip of a needle of the delivery device which carries the implant. Thus, the implant may be inserted directly into the eyeball without the need for any separate piercing step, resulting in cost and time savings.
In a method for manufacturing an intraocular implant according to the invention, two tubes of different diameters are utilized. The smaller tube is able to fit inside the longitudinal bore of the larger tube. When the tubes are cut, the smaller tube forms the tube of the implant and the remaining portions of the larger tube form the retention projection and disk of the implant.
An intraocular implant according to the invention provide the advantages of a full thickness fistula, while avoiding the limitations of the standard trabeculectomy. An implant according to the invention may be very small and implantable without surgery. No surgery room or hospitalization is necessary, thereby reducing costs. Implantation is minimally invasive, simple and quick, requiring only local anesthesia. Retrobulbar anaesthesia is not necessary, and thus iatrogenic damage to the optic nerve is avoided. There is no need to perform an iridectomy, and thus aqueous flow is maintained, lens nourishment is unaffected, and the likelihood of cataracts developing as a result of the procedure is reduced.
An implant according to the invention has other applications aside from the field of intraocular implants. For example, the implant may be used for drainage of a hydrocele sac, regulating flow between the hydrocele sac and the subcutaneous scrotum. As will be appreciated by persons of ordinary skill in the art, other applications of an implant in accordance with the invention are possible.